The present invention relates to the preparation of semiconductor device structures. More particularly, the present invention pertains to methods of forming high dielectric constant films, such as barium-strontium-titanate films.
Various dielectric films have been formed in the past during the fabrication of semiconductor devices. For example, films such as silicon dioxide and silicon nitride have been used for dielectric films in the formation of capacitors, such as for memory devices including, for example, dynamic random access memories (DRAMs). With the shrinkage of minimum feature sizes of semiconductor devices, e.g., increase in memory cell density in DRAMs, there is a continuing challenge to maintain sufficiently high storage capacitance despite decreasing cell area. One way of increasing cell capacitance is through the use of different cell structures such as trench and/or stacked capacitors. However, as feature size continues to become smaller and smaller, development of improved materials for cell dielectrics, as well as the cell structure, have become important.
Conventional dielectrics such as silicon dioxide and silicon nitride may no longer be suitable for use in many devices because of their relatively small dielectric constants. Insulating inorganic metal oxide materials, e.g., ferroelectric materials and perovskite oxides, have gained interest for use as dielectrics in memory devices. Generally, these materials have high dielectric constants which make them attractive as dielectric materials in capacitors, for example, for high density DRAMs and other memory devices. As used in this document, a high dielectric constant refers to a dielectric constant of about 15 or greater. For example, such high dielectric constant materials include tantalum pentoxide (Ta2O5), barium-strontium-titanate (BST), strontium titanate (SrTiO3), barium titanate (BaTiO3), lead zirconium titanate (PZT), and strontium-bismuth-tantalate (SBT). Using such materials enables the creation of much smaller and simpler capacitor structures for a given storage charge requirement, enabling an increased packing density for memory devices.
The dielectric properties of such films are dependent on various film characteristics, such as the concentration of the components thereof, e.g., the concentration of titanium in a BST film. Further, certain high dielectric constant materials have better current leakage characteristics in capacitors than other high dielectric constant materials. In some materials, aspects of the high dielectric constant material might be modified or tailored to achieve a particularly high dielectric constant, which may unfortunately and undesirably also tend to hurt the leakage characteristics, e.g., increased leakage current. For example, with respect to metal oxides having multiple different metals bonded with oxygen, such as BST, PZT, and SBT, it is found that increasing titanium concentration of the components thereof results in different dielectric characteristics. For example, with respect to BST films, it is found that increasing titanium concentration as compared to barium and/or strontium results in improved leakage characteristics, but decreases the dielectric constant. Accordingly, capacitance can be increased by increasing the concentration of barium and/or strontium, but unfortunately at the expense of an increasing leakage current. Further, absence of titanium in the oxide lattice creates a metal vacancy in such multi-metal titanates which can increase the dielectric constant but unfortunately also increases the current leakage.
It is desirable to form such high dielectric constant films by chemical vapor deposition (CVD) at low deposition temperatures, i.e., less than 680xc2x0 C. However, although step coverage is better at such low deposition temperatures, deposition rates for the high dielectric constant films is generally lower. Although an increase in deposition rate may occur at higher temperatures, such an increase in temperature over 680xc2x0 C. may damage barrier materials used in conjunction with the high dielectric constant films.
Generally, at low deposition temperatures, incorporation efficiency of components in the film are affected. For example, relative to high deposition temperature processes for forming BST films, incorporation efficiency of titanium in the formation of such high dielectric constant films decreases in conventional low deposition temperature processes. In fact, the stoichiometry of the high dielectric constant films appear to be self-adjusting in low deposition temperature processes. In other words, changing precursor flow ratios does not affect film composition at lower deposition temperatures, unlike the significant effect such changing of precursor flow ratios has in high temperature CVD processes. For example, with respect to BST films, a change in precursor flow ratio (e.g., Ba/Sr to Ti ratio) does not substantially affect film composition of a deposited BST film at temperatures less than 680xc2x0 C.
In many circumstances, it may be desirable to have varied concentrations within a high dielectric constant film (in other words, for example, changing the stoichiometry of different layers or portions of a BST film as it is deposited) deposited using low deposition temperature CVD processes. Since film composition is not affected by the conventional method of changing precursor flows, new methods of controlling the stoichiometry of high dielectric constant films are needed. Further, even if a film""s stoichiometry is controlled to a certain degree by changing precursor flow, the control of stoichiometry by changing precursor flow is disadvantageous in that, for example, extensive time for conditioning is required to change such flows.
The present invention provides the ability to control stoichiometry of dielectric films, e.g., high dielectric constant BST films, preferably at low deposition temperatures. For example, a deposition process according to the present invention may use an adjustment in oxidizer flow and/or partial pressure, the provision of a hydrogen-containing component, an adjustment in hydrogen-containing component flow and/or partial pressure, an adjustment in deposition pressure, and/or a modification of system component parameters (e.g., heating a shower head or adjusting a distance between a shower head of the deposition system and a wafer upon which the film is to be deposited), to control the high dielectric constant film characteristics, e.g., film stoichiometry.
A method for depositing a film according to the present invention includes providing a substrate assembly having a surface in a deposition chamber, preferably at a temperature less than 680xc2x0 C. A barium-containing organometallic precursor, a strontium-containing organometallic precursor, a titanium-containing organometallic precursor, and optionally at least one oxidizer and at least one hydrogen-containing composition are provided to the deposition chamber. A barium-strontium-titanate film is formed on at least a portion of the surface using the barium-containing organometallic precursor, the strontium-containing organometallic precursor, the titanium-containing organometallic precursor, and optionally the at least one oxidizer and/or the at least one hydrogen-containing composition provided to the deposition chamber. The barium-strontium-titanate film formed includes at least a first layer of the barium-strontium-titanate film having a first composition and at least a second layer of the barium-strontium-titanate film having a second composition.
The formation of the film is controlled in one or more various manners. For example, the deposition process may be controlled by adjusting the flow rate of the at least one oxidizer to the deposition chamber and/or a partial pressure of the at least one oxidizer in the deposition chamber during formation of the barium-strontium-titanate film such that composition of the barium-strontium-titanate film is adjusted from the first composition to the second composition. The oxidizer provided to the deposition chamber may be at least one of O2, O3, N2O, NO, SO3, H2O2, R2O2, where R is selected from a group consisting of a saturated or unsaturated linear, branched, or cyclic hydrocarbon group having about 1 carbon atom to about 20 carbon atoms, preferably about 2 carbon atoms to about 12 carbon atoms, for example, methyl, ethyl, isopropyl, t-butyl, heptyl, dodecyl, octadecyl, amyl, 2-ethythexyl, and the like.
Further, the deposition process may be controlled by adjusting a deposition pressure of the deposition chamber during formation of the barium-strontium-titanate film.
Yet further, the deposition chamber may include a delivery device having a delivery outlet region. The deposition process may then be controlled by adjusting a distance between the delivery outlet region of the delivery device and the surface of the substrate assembly during formation of the barium-strontium-titanate film and/or by adjusting a temperature of at least the delivery outlet region of the delivery device during formation of the barium-strontium-titanate film;
In addition, the depoisition process may be controlled by adjusting the flow rate of the at least one hydrogen-containing composition provided to the deposition chamber and/or a partial pressure of the at least one hydrogen-containing composition in the deposition chamber during formation of the barium-strontium-titanate film. The hydrogen-containing composition may include one or more of H2, NH3, N2H4, N2H3(CH3), and H2O.
Such adjustments to the process may be performed while maintaining a flow rate of the barium-containing organometallic precursor, strontium-containing organometallic precursor, and the titanium-containing organometallic precursor provided to the deposition chamber.
In one embodiment of the method, the first layer of the barium-strontium-titanate film is an interfacial layer and the second layer of the barium-strontium-titanate film is a bulk layer. The interfacial layer has an atomic percent of titanium less than or equal to the atomic percent of titanium in the bulk layer of the barium-strontium-titanate film.
In another embodiment, the adjusting of the deposition pressure of the deposition chamber during formation of the barium-strontium-titanate film while a flow rate of the barium-containing 6organometallic precursor, the strontium-containing organometallic precursor, and the titanium-containing organometallic precursor to the deposition chamber is maintained is such that composition of the barium-strontium-titanate film is adjusted from the first composition to the second composition. Further, with an increase in deposition pressure, an increase in percent titanium in the barium-strontium-titanate film and also an increase in a rate of deposition of the barium-strontium-titanate film can be attained.
The deposition processes described above may be used to form a barium-strontium-titanate dielectric film for use in formation of a capacitor. In other words, a first electrode having a surface in a deposition chamber is provided, a barium-strontium-titanate dielectric film is formed on at least a portion of the surface of the first electrode, and thereafter, a second electrode is formed on at least a portion of the barium-strontium-titanate dielectric film.
Similar methods as described above may be used to form an ABO3 dielectric film. For example, a substrate assembly having a surface may be provided in a deposition chamber at a temperature less than 680xc2x0 C. A plurality of precursors including A and B and an oxidizer (and optionally, at least one hydrogen-containing composition) are provided to the deposition chamber having the substrate assembly positioned therein to deposit a film of ABO3 on at least a portion of the surface of the substrate assembly. One or more of the control techniques described above may be used during deposition of the ABO3 film to produce different concentrations of one of A and B at different elevations in the ABO3 film.
In various embodiments, the different concentrations include a concentration in a first layer of the ABO3 film that is different from a concentration of a second layer of the ABO3 film and/or the different concentrations are a gradient in concentrations in at least a portion of the ABO3 film.
The above summary of the present invention is not intended to describe each embodiment or every implementation of the present invention. Advantages, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.